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At the age of five Henri suffered a bad setback from diph-
theria which left him for nine months with a paralyzed larynx.
This misfortune made him for long delicate and timid, but it
also turned him back on his own resources as he was forced to
shun the rougher games of children his own age.
His principal diversion was reading, where his unusual talents
first showed up. A book once read - at incredible speed - became
a permanent possession, and he could always state the page and
line where a particular thing occurred. He retained this power-
ful memory all his life. This rare faculty, which Poincare shared
with Euler who had it in a lesser degree, might be called visual
or spatial memory. In temporal memory - the ability to recall
with uncanny precision a sequence of events long passed - he
was also unusually strong. Yet he unblushingly describes his
memory as 'bad'. His poor eyesight perhaps contributed to a
third peculiarity of his memory. The majority of mathemati-
cians appear to remember theorems and formulae mostly by
eye; with Poincare it was almost wholly by ear. Unable to see
the board distinctly when he became a student of advanced
mathematics, he sat back and listened, following and remem-
bering perfectly without taking notes - an easy feat for him,
but one incomprehensible to most mathematicians. Yet he
must have had a vivid memory of the 'inner eye' as well, for
much of his work, like a good deal of Riemann's, was of the
kind that goes with facile space-intuition and acute visualiza-
tion. His inability to use his fingers skilfully of course handi-
capped him in laboratory exercises, which seems a pity, as some
of his own work in mathematical physics might have been closer
to reality had he mastered the art of experiment. Had Poincare
been as strong in practical science as he was in theoretical he
might have made a fourth with the incomparable three*
Archimedes, Newton, and Gauss.
Not many of the great mathematicians have been the absent-
minded dreamers that popular fancy likes to picture them.
Poincare was one of the exceptions, and then only in compara-
tive trifles, such as carrying off hotel linen in his baggage. But
many persons who are anything but absent-minded do the
same, and some of the most alert mortals living have even been